This invention relates generally to injection molding and more particularly to a method of making an integral nozzle with an integral heating element extending outward between adjacent collar portions.
Injection molding nozzles having a helical integral electrical heating element extending around the central melt bore are well known in the art. As seen in the applicant's U.S. Pat. No. 4,865,535 which issued Sep. 12, 1989, it is also known to have a portion of the heating element swaged back upon itself to provide more heat in certain areas. Of course, each nozzle must have a terminal to which external lead wires are connected to provide power to the heating element. In the past, this has usually been provided by the heating element having end portions which extend outward through a radial opening in a collar portion adjacent the rear end of the nozzle. An example of this is seen in the applicant's U.S. Pat. No. 4,386,262 which issued May 31, 1983. In this case, a so called "hot" terminal is formed by casting beryllium copper around the heating element in a radially extending sleeve. While this terminal is structurally sound, it has the disadvantage that the terminal is too hot which results in possible damage due to overheating of the external lead wires or other adjacent materials. Another example of the end portions of the heating element extending outward through an opening in the collar portion is shown in the applicant's U.S. Pat. No. 4,403,405 which issued Sep. 13, 1983. In this case, half washers mounted in the opening around the heating element prevent the conductive beryllium copper flowing out into the terminal. While this overcomes the problem of the terminal overheating and thus is a so called "cold" terminal, it has the disadvantage that the terminal is not as strong structurally and it is difficult to ensure the terminal extends straight out from the nozzle.
Another example of a method of making a terminal in which the end portion of a heating element has to be run out through a hole in the collar portion is described in the applicant's U.S. Pat. No. 4,837,925 which issued Jun. 13, 1989. However, it is relatively easy to manipulate the end portion of the heating element because it is a low voltage application with the other end of the heating element grounded to the nozzle body and thus there is only a single terminal wire extending to the terminal. Reliable terminals having two terminal wires are more difficult to make than terminals having only a single terminal wire because it is important that the two projecting terminal wires of the heating element extend parallel to each other and are spaced apart a predetermined distance. Also, the terminal must be structurally secure and relatively easy to manufacture without requiring two different brazing steps.